Our goal is to study the mechanisms of immune defense against tumors. Over the past year we have carried out the following projects: (1) studies on the biochemical mechanisms of macrophage activation; (2) purification and characterization of a cytotoxic factor from activated macrophages and studies on the mechanisms of action of this factor; (3) studies on the mechanisms of chemoattractant action of lysophosphatidylcholine on lymphocytes; and (4) characterization of monoclonal antibodies against human leukemia-associated antigens. (MB)